In recent years, a method of immersing a solid-phase sheet growing substrate in the melt of a semiconductor material or metal material to form a solid-phase sheet on the surface of the solid-phase sheet growing substrate has been developed (for example, Patent Documents 1 and 2). According to this method, a plurality of solid-phase sheet growing substrates arranged at regular intervals are continuously immersed in the melt in a crucible. For example, in the case where a polycrystalline silicon sheet used for a solar cell as a solid-phase sheet is manufactured, in an inert atmosphere, a solid-phase sheet growing substrate is immersed in the melt in the crucible in which the high-purity silicon material having the dopant such as phosphorus or boron added thereto is heated and melted. This causes a polycrystalline silicon sheet to be formed on the surface of the solid-phase sheet growing substrate. The formed polycrystalline silicon sheet is peeled off from the solid-phase sheet growing substrate and cut into a desired size by a laser, a dicing saw or the like to provide a wafer for a solar cell.
FIG. 16 is a perspective view schematically showing the conventional solid-phase sheet growing substrate disclosed in Japanese Patent Laying-Open No. 2002-237465 (Patent Document 1). Referring to FIG. 16, a peripheral groove 10 is formed on the top surface of a solid-phase sheet growing substrate 100 in the figure, and a cut-out groove 170 is further formed on the right and left sides thereof in the figure. This configuration causes a surrounding portion 12 located at the outer side of peripheral groove 10 to be divided into two C-shaped portions.
FIG. 17 is a perspective view schematically showing the conventional substrate (solid-phase sheet growing substrate) disclosed in the pamphlet of International Publication No. 04/016836 (Patent Document 2), FIG. 18 is a cross-sectional view taken along the line XVIII-XVIII in FIG. 17 in the state where silicon is formed on the surface of the substrate (solid-phase sheet growing substrate).
Referring to FIG. 17, a trench structure F13 is formed on a substrate first surface 135A and a substrate second surface 136A. This trench structure F13 serves to separate the silicon grown on peripheral portions 135a and 136a from the portion of the plate-like silicon mainly used as a product. Since the surface tension between the silicon melt and a substrate C13 (solid-phase sheet growing substrate) is high, the silicon melt comes into contact with substrate first surface 135A and peripheral portion 135a but not with trench structure F13. Accordingly, as shown in FIG. 18, the plate-like silicon 131A crystallized and grown on the surface of substrate first surface 135A and the silicon crystallized and grown on the surface of peripheral portion 135a are separated with trench structure F13 interposed therebetween.
Furthermore, a substrate third surface 138A is formed on substrate C13 (solid-phase sheet growing substrate). Substrate first surface 135A, substrate second surface 136A and substrate third surface 138A constitute a three-surface structure, which causes the formed silicon to be engaged in substrate C13 (solid-phase sheet growing substrate).    Patent Document 1: Japanese Patent Laying-Open No. 2002-237465 (FIG. 7)    Patent Document 2: Pamphlet of International Publication No. 04/016836 (FIG. 13)